The player with the ball throws the ball up towards the net, setting themsleves up to then try and smash the ball onto the target mat.
The player on the other side of the net has to try and block the smash and stop it hitting the target.
The blocker should try to not only prevent the ball hitting the mat, but also ensure that the ball ends up the other side of the net.
New hitters rarely miss because of their arm. They miss because of their feet. Build a reliable approach, then time it with your setter.
When your hitter gets stuffed, five teammates standing and watching is how you lose the point. Good attack coverage turns a blocked ball into a second swing.
Coaches spend hours correcting arms in serve receive when the real fault is almost always the feet. Fix the movement and the platform fixes itself.